A group of Silicon Valley technologists who were early employees at Facebook and Google, alarmed over the ill effects of social networks and smartphones, are banding together to challenge the companies they helped build.

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The campaign, titled The Truth About Tech... will be aimed at educating students, parents and teachers about the dangers of technology, including the depression that can come from heavy use of social media.

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"We were on the inside," said Tristan Harris, a former in-house ethicist at Google who is heading the new group. "We know what the companies measure. We know how they talk, and we know how the engineering works."